A simple noise model of a microwave MESFET (MODFET, HEMT, etc.) is described and verified at room and cryogenic temperatures. Closed-form expressions for the minimum noise temperature, the optimum generator impedance, the noise conductance, and the generator-impedance-minimizing noise measure are given in terms of the frequency, the elements of a FET equivalent circuit, and the equivalent temperatures of intrinsic gate resistance and drain conductance to be determined from noise measurements. These equivalent temperatures are demonstrated in the case of a Fujitsu FHR01FH MODFET to be independent of frequency in the frequency range in which 1/f noise is negligible. Thus, the model allows prediction of noise parameters for a broad frequency range from a single frequency noise parameter measurement. The relationships between this approach and other relevant studies are established. >

Modeling of noise parameters of MESFETs and MODFETs and their frequency and temperature dependence

Exploring dynamics in the far-infrared with terahertz spectroscopy.

Experimental verification of analytic formulas for the dispersion and the attenuation of electrical transient signals propagating on coplanar transmission lines is presented. The verification is done in the frequency domain over a terahertz range although the experiments are in the time domain. The analytic formulas are obtained from fits to the full-wave analysis results. It is quantitatively verified that the full-wave steady-state solutions can be directly applied to the transient time-domain propagation experiments. Subpicosecond electrical pulses and an external electrooptic sampling technique are used to obtain the time-domain propagation data. From the Fourier transforms of the time-domain data both the attenuation and the phase information as a function of frequency are extracted. The dispersion and the attenuation characteristics are investigated for both coplanar waveguide and coplanar strip transmission lines. The investigation is carried out on both semiinsulating semiconductor and dielectric substrate materials. No observable losses caused by the semiconductor material are indicated. >

Terahertz attenuation and dispersion characteristics of coplanar transmission lines

We describe active and nonlinear wave propagation devices for generation and detection of (sub)millimeter wave and (sub)picosecond signals. Shock-wave nonlinear transmission lines (NLTL's) generate /spl sim/4-V step functions with less than 0.7-ps fall times. NLTL-gated sampling circuits for signal measurement have attained over 700-GHz bandwidth. Soliton propagation on NLTL's is used for picosecond impulse generation and broadband millimeter-wave frequency multiplication. Picosecond pulses can also be generated on traveling-wave structures loaded by resonant tunneling diodes. Applications include integration of photodetectors with sampling circuits for picosecond optical waveform measurements and instrumentation for millimeter-wave waveform and network (circuit) measurements both on-wafer and in free space. General properties of linear and nonlinear distributed devices and circuits are reviewed, including gain-bandwidth limits, dispersive and nondispersive propagation, shock-wave formation, and soliton propagation. >

Active and nonlinear wave propagation devices in ultrafast electronics and optoelectronics

We present an overview of solid-state integrated circuit amplifiers approaching terahertz frequencies based on the latest device technologies which have emerged in the past several years. Highlights include the best reported data from heterojunction bipolar transistor (HBT) circuits, high electron mobility transistor (HEMT) circuits, and metamorphic HEMT (mHEMT) amplifier circuits. We discuss packaging techniques for the various technologies in waveguide modules and describe the best reported noise figures measured in these technologies. A consequence of THz transistors, namely ultra-low-noise at cryogenic temperatures, will be explored and results presented. We also present a short review of power amplifier technologies for the THz regime. Finally, we discuss emerging materials for THz amplifiers into the next decade.

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An Overview of Solid-State Integrated Circuit Amplifiers in the Submillimeter-Wave and THz Regime

High electron mobility transistors (HEMTs) based on the InAlAs/InGaAs heterojunction grown lattice matched to InP were fabricated with 0.15 μm T-shaped gates. The use of an undoped InGaAs cap layer in the epitaxial structure leads to excellent gate characteristics and very high transistor gain. At 95 GHz, a maximum available gain of 13.6 dB was measured. A maximum frequency of oscillation fmax of 455 GHz was obtained by extrapolating from 95 GHz at –6 dB/octave. This is the best reported gain performance for any transistor.

Extremely high gain 0.15 mu m gate-length InAlAs/InGaAs/InP HEMTs

Quarter-micrometer gate-length high-electron-mobility transistors (HEMTs) for cryogenic low-noise application with very low light sensitivity have been developed. At room temperature, these exhibit a noise figure of 0.4 dB with associated gain of 15 dB at 8 GHz. At a temperature of 12.5 K the minimum noise temperature of 5.3+or-1.5 K has been measured at 8.5 GHz, which is the best noise performance observed to date for any microwave transistors. The results clearly demonstrate the potential for low-temperature low-noise applications. >

Ultra-low-noise cryogenic high-electron-mobility transistors

0.15- mu m-gate-length double-heterojunction pseudomorphic high electron mobility transistors (HEMTs) for which excellent millimeter-wave power and noise performance were achieved simultaneously are reported. The 50- mu m-wide HEMTs yielded record maximum power-added efficiencies of 51, 41, and 23% at 35, 60, and 94 GHz, respectively. Maximum output powers of 139 mW at 60 GHz and 57 mW at 94 GHz were also measured for 150- mu m-gate-width devices. Finally, minimum noise figures as low as 0.55 and 1.8 dB were measured at 18 and 60 GHz respectively. This is the best power and noise performance yet reported for passivated transistors at millimeter-wave frequencies. >

Very high power-added efficiency and low-noise 0.15- mu m gate-length pseudomorphic HEMTs

High electron mobility transistors (HEMTs) have demonstrated unsurpassed transistor performance in the millimeter-wave range--at 60 GHz, results include a minimum noise figure of 2.3 dB with 4.0 dB associated gain, maximum small-signal gain of 11.7 dB, output power of 50 mW, power density of 0.43 W/mm and maximum power-added efficiency of 28%. The principles of HEMT operation and design are described, followed by a summary of the current state-of-the-art in noise and power performance, and discussion of several applications.

Advances in HEMT Technology and Applications

We report the successful growth of high quality molecular beam epitaxy (MBE) GaAs, AlGaAs, AlGaAs/GaAs modulation doped heterostructures and a GaAs/InGaAs/GaAs quantum well on GaAs (111)B substrates. Modulation doped heterostructures show a 77 K mobility of 145 500 cm2/V s with a sheet density of 5.0×1011 cm−2. Photoluminescence of (111)B GaAs indicates a lower carbon incorporation than achieved on (100) substrates. The low growth temperature and high material quality obtainable in (111)B growth will provide advantages for laser diodes and heterostructure field effect transistors.

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J.M. Ballingall

Papers

Extremely high gain 0.15 mu m gate-length InAlAs/InGaAs/InP HEMTs

Ultra-low-noise cryogenic high-electron-mobility transistors

Very high power-added efficiency and low-noise 0.15- mu m gate-length pseudomorphic HEMTs

Advances in HEMT Technology and Applications

High quality (111)B GaAs, AlGaAs, AlGaAs/GaAs modulation doped heterostructures and a GaAs/InGaAs/GaAs quantum well